public class MyIdeaListExtension1 {
    public MyIdeaListExtension1(ApexPages.StandardSetController controller) {

    }

    private final ApexPages.IdeaStandardSetController ideaSetController; 

    public MyIdeaListExtension1 (ApexPages.IdeaStandardSetController controller) {
        ideaSetController = (ApexPages.IdeaStandardSetController)controller;
    }

    public List<Idea> getModifiedIdeas() {
        Idea[] ideas = ideaSetController.getIdeaList();
        // modify ideas here 
            return ideas;
    }
}